Why does the motor vibrate? What are the maintenance measures?

02/11/2019

Generally, motors with more than 8 poles do not cause vibration due to motor manufacturing quality problems. Vibration is common in 2-6 pole motors, GB10068-2000.

The "Rotating Motor Vibration Limits and Test Methods" stipulates the vibration limit, measurement method and rigidity basis of different center high motors on the basis of rigidity. According to this standard, it can be judged whether the motor meets the standard.

Harm of motor vibration

The vibration of the motor will shorten the insulation of the winding and the bearing life, affecting the normal lubrication of the sliding bearing. The vibration force will expand the insulation gap, and the external dust and moisture will invade it, causing the insulation resistance to decrease and the leakage current to increase, even forming insulation breakdown. Waiting for an accident.

In addition, the motor generates vibration, and it is easy to cause the cooler water pipe to crack, the welding point to vibrate, and damage to the load machinery, reduce the accuracy of the workpiece, cause fatigue of all mechanical parts subjected to vibration, and loosen the anchor screw. Or break it.

The vibration of the motor will cause abnormal wear of the carbon brush and the slip ring. Even the severe brushing will burn the collector ring insulation, and the motor will generate a lot of noise. This situation usually occurs in the DC motor.

Cause of vibration

There are three main situations:
Electromagnetic reasons; mechanical reasons; mechanical and electrical mixing reasons.

First, the electromagnetic reasons

1. Power supply: The three-phase voltage is unbalanced, and the three-phase motor is out of phase.

2, the stator: the stator core becomes elliptical, eccentric, loose; the stator winding breaks, grounding breakdown, turn-to-turn short circuit, wiring error, stator three-phase current imbalance.

3, the rotor failure: the rotor core becomes elliptical, eccentric, loose. The rotor cage strip is welded to the end ring, the rotor cage strip is broken, the winding is wrong, and the brush is in poor contact.

Second, mechanical reasons

1, the motor itself

The rotor is unbalanced, the shaft is bent, the slip ring is deformed, the stator and rotor air gaps are uneven, the stator and rotor magnetic centers are inconsistent, the bearing is faulty, the basic installation is poor, the mechanical mechanism is not strong enough, the resonance is loose, the ground screw is loose, and the motor fan is damaged.

2, with the coupling aspect

The coupling is damaged, the coupling is poorly connected, the coupling is not centered, the load is mechanically unbalanced, and the system is resonant. The linkage part of the shaft system is misaligned, the center line does not coincide, and the centering is incorrect. The cause of this failure is mainly caused by poor alignment and improper installation during the installation process.

There is also a case where some of the center lines of the interlocking parts are coincident in the cold state, but after a period of operation, the center line is broken due to the deformation of the rotor fulcrum and the foundation, thereby generating vibration.

Third, the reason for motor mixing

1. Motor vibration is often caused by uneven air gap, which causes single-sided electromagnetic pulling force, and the single-sided electromagnetic pulling force further increases the air gap. This electromechanical mixing acts as motor vibration.

2. The axial movement of the motor is caused by the gravity or the installation level of the rotor itself and the magnetic center is not correct. The electromagnetic tension caused by the motor causes the axial movement of the motor to cause the motor vibration to increase. In severe cases, the shaft is ground and the temperature of the bearing is increased. Rapidly rises. Gears and couplings associated with the motor are faulty. This kind of failure mainly manifests as poor gear occlusion, serious tooth wear, poor lubrication of the wheel, skewing and misalignment of the coupling, tooth profile of the gear coupling, incorrect tooth pitch, excessive clearance or serious wear, which will cause certain vibration.

Defects in the structure of the motor itself and installation problems. This kind of failure mainly manifests as the ellipse of the journal, the bending of the shaft, the gap between the shaft and the bearing bush is too large or too small, and the rigidity of the bearing seat, the foundation plate, a part of the foundation and even the entire motor installation base is insufficient, and the motor and the base plate are fixed. Not secure, the foot bolts are loose, and the bearing housing and the base plate are loose. The excessive or too small gap between the shaft and the bearing bush can not only cause vibration but also cause abnormal lubrication and temperature of the bearing bush.

3. Load-driven vibration of motor drag

How to find the cause of vibration

1. Before the motor is not stopped, check the vibration of each part with the vibration meter. For the vibration part, test the vibration value in three directions of vertical horizontal axis. If the ground screw is loose or the bearing end cover screw is loose, Directly tighten, measure the vibration after tightening, and observe whether it is eliminated or lightened.

Secondly, it is necessary to check whether the three-phase voltage of the power supply is balanced, and whether the three-phase fuse has a blown phenomenon. The single-phase operation of the motor can not only cause vibration, but also cause the temperature of the motor to rise rapidly, and observe whether the current meter pointer swings back and forth, and the rotor is broken. There is a current swing phenomenon.

Finally, check whether the three-phase current of the motor is balanced. If problems are found, contact the operation personnel in time to stop the motor running, so as not to burn the motor.

2. If the motor vibration is not solved after the surface phenomenon is processed, continue to disconnect the power supply, uncoupling the coupling, and separate the load connected to the motor, and turn the motor.

If the motor itself does not vibrate, it means that the vibration source is caused by the coupling not being aligned or the load machine. If the motor vibrates, it means that the motor itself has a problem.

In addition, the power-off method can be used to distinguish between electrical reasons and mechanical reasons. When the power is cut off, the motor does not vibrate or the vibration is relieved immediately, indicating that it is an electrical cause, otherwise it is a mechanical fault.

Overhaul for the cause of the failure

1. Overhaul of electrical causes:

The first is to determine whether the three-phase DC resistance of the stator is balanced. If it is unbalanced, it means that the welding part of the stator is welded, the winding is separated by phase, and the winding is short-circuited. If the fault is obvious, it can be insulated. The surface is burnt, or the stator winding is measured with an instrument. After confirming the short circuit between turns, the motor winding is re-routed.

2. Maintenance of mechanical reasons:

Check that the air gap is uniform. If the measured value is exceeded, re-adjust the air gap. Check the bearing, measure the bearing clearance, if it is not qualified to replace the new bearing, check the core deformation and looseness, the loose iron core can be bonded with epoxy resin glue, check the rotating shaft, repair the reaming of the curved shaft or directly straight shaft And then do the balance test on the rotor

3. Overhaul of the load mechanical part:

If the motor itself has no problem, then the cause of the fault is caused by the connection part. At this time, check the basic level of the motor, the inclination, the strength, whether the center is correct, whether the coupling is damaged, and whether the motor shaft extension is Meet the requirements and so on.

Steps to handle motor vibration

1. Disconnect the motor from the load, test the motor for air, and check the vibration value.

2. Check the vibration value of the motor foot. According to the national standard GB10068-2006, the vibration value at the foot plate should not be greater than 25% of the corresponding position of the bearing. If the value exceeds this value, the motor foundation is not a rigid foundation.

3. If there are only one or four diagonal vibrations of the four feet, the loosening of the anchor bolts will cause the vibration to pass, indicating that the underfoot is not properly ground, and the anchor bolts are tightened to cause vibration of the base. Put the foot on the ground, realign the centering and tighten the anchor bolts.

4. Fully tighten the four anchor bolts on the foundation. The vibration value of the motor still exceeds the standard. At this time, check whether the coupling of the shaft extension is flat with the shoulder. If it is not flat, the shaft is extended with extra keys. The exciting force will cause the horizontal vibration of the motor to exceed the standard.

In this case, the vibration value is not too much, and the vibration value can be lowered after docking with the host. It should be convinced to be used by the user. The two-pole motor is installed in the semi-key in the shaft extension keyway according to GB10068--2006 in the factory test. Excess keys will not add extra excitability. If you need to deal with it, just cut the extra key to the length of the general.

5. If the vibration test of the motor is not exceeded, the vibration of the load exceeds the standard, there are two reasons: one is that the deviation is relatively large;

The other is that the residual unbalance of the rotating part (rotor) of the main engine overlaps with the phase of the residual unbalance of the rotor of the motor. After the docking, the residual unbalance of the entire shaft is at the same position, and the generated exciting vibration force causes vibration. . At this time, the coupling can be disengaged, and any one of the two couplings can be rotated by 180 ° C, and then the vibration of the test machine can be lowered.

6, vibration vibration speed (intensity) does not exceed the standard, vibration acceleration exceeds the standard, can only replace the bearing.

7. Due to the poor rigidity of the rotor of the two-maximum power motor, it will be deformed without using the rotor for a long time, and may vibrate when it is rotated. This is the reason for the poor storage of the motor. Under normal circumstances, the storage of the two-pole motor. Every 15 days, the motor should be driven, and each time the car is rotated at least 8 times.

8. The motor vibration of the sliding bearing is related to the assembly quality of the bearing bush. It should be checked whether the bearing bush has a high point, whether the bearing oil of the bearing bush is sufficient, the bearing bushing force, the bearing bush clearance, and the magnetic center line are suitable.

9. Under normal circumstances, the reason of motor vibration can be judged from the vibration value in three directions, the horizontal vibration is large, the rotor is unbalanced; the vertical vibration is large, the installation foundation is not flat; the axial vibration is large, the bearing assembly low quality.

This is just a simple judgment. According to the situation on the spot, combined with the factors mentioned above, comprehensive consideration should be made to find the real cause of the vibration.

10, Y series box motor vibration should pay special attention to axial vibration, such as axial vibration is greater than radial vibration, the damage to the motor bearing is extremely great, will cause the axle accident.

Pay attention to the bearing temperature. If the positioning bearing is faster than the non-locating bearing, stop it immediately. This is because the axial vibration caused by the axial rigidity of the base is insufficient, and the base should be reinforced.

11. After the rotor is dynamically balanced, the residual unbalance of the rotor has solidified on the rotor and will not change. The vibration of the motor itself will not change with the change of the location and working conditions. The vibration problem can be handled at the user site. of.

Under normal circumstances, the maintenance motor does not need to perform dynamic balance check on the motor. Except for the special case, such as flexible foundation and rotor deformation, it must be dynamically balanced or returned to the factory for processing.